Downhole tools are used for operations inside boreholes of oil and gas wells. Downhole tools operate in a very harsh environment and must be able to withstand inter alia corrosive fluids, very high temperatures and pressure.
To avoid unnecessary and expensive disturbances in the production of oil and gas, the tools deployed downhole have to be reliable and easy to remove from the well in case of a breakdown. Tools are often deployed at great depths several kilometers down the well, and removing jammed tools are therefore a costly and time-consuming operation.
Well tools are often part of a larger tool string containing tools with different functionalities. A tool string may comprise both transportation tools for transporting the tool string in the well and operational tools for performing various operations downhole.
Various principles for downhole transportation tools, also denoted well tractors, have been developed and tested. The transportation tools are primarily used for transporting tool strings in horizontal or close to horizontal parts of the well where gravity is insufficient for driving the tool string forward.
The operation conditions of downhole tools require that the tools are properly serviced on a regular basis, e.g. between each operation downhole. Maintenance and repair time is often expensive as it prolongs the time for performing operations downhole and possible time without production on an oil rig. Therefore, a need exists for downhole tools that are easy and fast to service.